The present invention relates to a magnetic disk drive.
Thickness of a lubricant film applied onto a surface of magnetic disk is decreased on account of a centrifugal force and a shear force generated by rotation of the magnetic disk, and splashing by temperature rise in the magnetic disk drive. In order to maintain sliding durability between a magnetic disk and a magnetic head slider, a lubricant is supplied onto surface of the disk, or the lubricant is applied onto the surface of the disk. Various methods for supplying lubricants onto the surface of disk in a magnetic disk drive are disclosed in JP-A-59-218668 (1984), JP-A-60-239921 (1985), JP-A-8-45238 (1996), JP-A-10-312660 (1998), JP-A-8-45239 (1996), JP-A-6-295579 (1994), Japanese Patent No. 2796852, and others.
In accordance with JP-A-59-218668 (1984), a lubricant is supplied onto the surface of magnetic disk from a venting hole at the center of the hub by generating the lubricant vapor from the lubricant impregnated member provided at the bottom of the device by heated air flow generated with rotation of the magnetic disk. In accordance with JP-A-60-239921 (1985), a lubricant film is formed on the surface of magnetic disk by depositing from myristic acid vapor, which is vaporized from a myristic acid impregnated member by blowing hot air thereon. In accordance with JP-A-8-45238 (1996), a lubricant film made of a liquid lubricant is formed on an arm or a suspension, and the lubricant is supplied onto the surface of magnetic disk by an air flow accompanied with rotation of the magnetic disk. In accordance with JP-A-10-312660 (1998), JP-A-8-45239 (1996), and Japanese Patent No. 27906852, a liquid lubricant is supplied onto the surface of magnetic disk by placing a wick material, wherein the liquid lubricant having a low viscosity is impregnated, in the vicinity of the disk. In accordance with JP-A-6-295579 (1994), a lubricant is supplied from a reservoir provided with a heating element.
Thickness of lubricant film on the disk maintains a definite value under a condition that an amount of the lubricant reduced by scraping-off and splashing is balanced with an amount of the lubricant supplied by heat and air flow, and sliding durability between the magnetic disk and the magnetic head slider is ensured. However, if the balance is lost, the lubricating performance is lowered by continuous decrease of the lubricant film thickness, or reversely, too much increase of the lubricant film thickness. Furthermore, another cause for decreasing the sliding performance is contamination of the head slider with various contaminants which are brought into the device from both exterior and interior of the device.
In order to solve the problem mentioned above, by supplying a lubricant, physical properties of the lubricant such as molecular structure and molecular weight, and the amount of the lubricant held in the magnetic disk drive must be studied in detail before practical use of the lubricant. In accordance with the prior art mentioned above, optimization of supplying amount of the lubricant, physical properties of the lubricant such as molecular structure and molecular weight, and the amount of the lubricant held in the magnetic disk drive are not practically studied nor disclosed. Accordingly, stable supply of the lubricant by heat or air flow is impossible.
Furthermore, operation systems and structures of the magnetic disk drive must be considered. For instance, in accordance with a CSS (Contact Start Stop) system disclosed in JP-A-59-218668 (1984), a strong adsorption (stiction)is generated between the head slider and the magnetic disk, if the lubricant film thickness is increased, and a trouble such as difficulty in starting up of the magnetic disk and the like are generated. Therefore, a L/UL (Load/Unload) system can be deemed as desirable for supplying a lubricant.
One of the objects of the present invention is to provide a magnetic disk drive having a small decrease in thickness of lubricant film on the magnetic disk surface, and a superior reliability in sliding performance between the magnetic head and the magnetic disk surface.
In order to decrease reduction of lubricant film thickness on the magnetic disk surface, the inventors of the present invention found an optimum molecular weight and molecular structures of lubricants which are supplied from a lubricant holding member to the magnetic disk surface utilizing heat in the magnetic disk drive and an air flow caused by rotation of the magnetic disk. Furthermore, the lubricant holding members were studied and optimized.
When the lubricant is supplied utilizing heat and/or air flow, the amount of supplied lubricant varies significantly depending on the material which holds the lubricant, and direction, strength, temperature, and the like of air flow at the installed location of the lubricant holding member. Necessary amount of the lubricant varies depending on the volume of the magnetic disk drive, a number of rotation of the disk, and the number of magnetic disks mounted on the magnetic disk drive. In order to optimize the supplying amount of the lubricant, the molecular weight and the molecular structure of the lubricant must be specified, because physical properties of the lubricant varies depending on the molecular weight and the molecular structure.
Perfluoropolyether, one of the lubricants for the magnetic disk, is less volatile in comparison with hydrocarbon group lubricants such as mineral oil and the like which are used for general industrial machines. In accordance with increasing molecular weight, the lubricant becomes less volatile. Accordingly, in order to supply perfluoropolyether to surface of the disk by heat and air flow, readily volatile relatively low molecular weight components are necessary.
Furthermore, the structure of terminal group of the lubricant must be specified in order to optimize the supplying amount of the lubricant, because an adsorbing force of the lubricant holding member and mutual interactions between the lubricant molecules themselves vary significantly depending on the structure of the terminal group of perfluoropolyether molecules. The adsorbing force between the lubricant holding member and the lubricant influences on readiness of supplying the lubricant, and the mutual interactions between the lubricant molecules themselves influence on recovery of the lubricant film on surface of the magnetic disk.
Lubricants, which can reduces as possible to adhere gases brought into the magnetic disk drive, gases, wear particle, and dusts generated in the device onto sliding portions of the slider and head element portions, are desirably selected.
Feature of the present invention is that: a lubricant supplying means for supplying a lubricant to surface of the magnetic disk from a portion other than the surface of the disk is provided in the magnetic disk drive; the lubricant supplied by the lubricant supplying means includes at least one of the components expressed by the structural formulas 1-5; and the component is perfluoropolyether having a molecular weight equals to or smaller than 4000. Furthermore, desirably, the components having a molecular weight of at least 1000 and equals to or smaller than 4000 are contained at least 40%. 
The lubricant supplying means can be a suspension or an arm applied with the lubricant.
The lubricant supplying means can be a lubricant holding means which holds the lubricant. In this case, the lubricant desirably contains perfluoropolyether having a structure expressed by any one of the structural formulas 1-5. The lubricant holding means is desirably made of a material, which can hold the lubricant without separating as the lubricant drops, such as filter, wick materials, and the like.
The lubricant holding means is desirably a filter impregnated with perfluoropolyether having a structure expressed by any one of the structural formulas 1-5. In this case, at least 0.15 xcexcl of perfluoropolyether having a structure expressed by any one of the structural formulas 1-5 is impregnated, in order to reduce the amount of contaminant adhered to a levitated plane of the magnetic head slider.
In order to reduce the amount of contaminant adhered to the levitated plane of the magnetic head slider and, further, to reduce decrease of the lubricant film thickness, at least 0.5xcexc-liter of perfluoropolyether having a structure expressed by any one of the structural formulas 1-5 is desirably impregnated. The amount of the lubricant impregnated into the filter does not have any particular limitation as far as the lubricant does not cause any trouble in operation of the device such as generating lubricant drops and the like, and the amount of the lubricant is decided in consideration of the recovery effect of the lubricant film.
If the lubricant film formed on the magnetic disk contains at least one of perfluoropolyether having structures expressed by the structural formulas 1-5, the lubricant supplied from the lubricant supplying means is readily adhered onto the lubricant film formed on the magnetic disk surface, and a high recovery effect of the lubricant film is realized.
As for an operation system of the magnetic disk drive comprising a lubricant supplying means, the conventional CSS (Contact Start Stop) system has an effect to prevent head crash and others. However, the L/UL system; in which the magnetic head slider is positioned above the magnetic disk plane only when the magnetic disk is rotating, and the magnetic head slider is escaped to an outer region from the outer peripheral plane of the magnetic disk when the rotation of the magnetic disk is stopped; is advantageous because any problems such as adsorption (stiction) and the like will not be generated.
As explained above, sliding durability between the magnetic disk and the magnetic head slider can be ensured by supplying the lubricant from a lubricant supplying means. Furthermore, the lubricant can be supplied stably, and any significant design change of the device and increase in number of the components are unnecessary.